1. Field of the Invention
This invention relates to a contact terminal which is so designed that, when a covered conductor (or electrical wire) is press-fitted into a slot, the internal conductor is brought into contact with the terminal without removal of the insulating cover of the covered conductor.
2. Background
FIG. 7 is a perspective view showing a conventional contact terminal disclosed by Unexamined Japanese Patent Publication No. Sho. 59-226477.
In FIG. 7, reference numeral 1' designates the aforementioned conventional contact terminal. The contact terminal 1' is formed integrally by pressing a thin metal plate which is punched. The front end portion of the contact terminal is an electrical contact section 2' which is engaged with a mating terminal, and its rear end portion is a wire clamping section 3', and the middle portion between the front and rear end portions is an electrically conductive section 4'. More specifically, the electrical conductive portion 2' is engaged with the mating terminal so as to be electrically connected with each other; the wire clamping section 3' has right and left retaining pieces (parts of the walls) 3a', which are bent inwardly to fixedly hold a wire W from the above; and the electrically conductive section 4' is electrically connected to the conductor of the wire W. The wire clamping section 3' is coupled through a first neck 7" to the electrically conductive section 4', and the electrically conductive section 4' is coupled through a second neck 7' to the electrical contact section 2'.
The electrically conductive section 4' has a front insulation piercing portion 10A' and a rear insulation piercing portion 10B' which are arranged at the front and rear ends thereof. The front insulation piercing portion 10A' has contact blades 11' and 11' which are confronted with each other in such a manner as to form a slot 12' between them into which the conductor (core) of the wire W is inserted. Similarly, the rear insulation piercing portion 10B' also has contact blades 11' and 11' which are confronted with each other in such a manner as to form a slot 12' between them into which the conductor of the wire W is inserted.
The wire clamping section 3', the electrically conductive section 4', and the electrical contact section 2' have a common bottom wall having the first neck 7" and the second neck 7'. The common bottom wall is a belt-shaped flat plate. The electrically conductive section 4' is substantially U-shaped in section. More specifically, the electrically conductive section 4' has a part of the common bottom wall which is provided between the first neck 7" and the second neck 7', and right and left side walls 9' and 9' which extend upwardly from the right and left edge portions of the bottom wall, respectively. The insulation piercing blades 11' of the insulation piercing portions 10A' and 10B' are respectively formed by bending inwardly the front and rear end portions of the side walls 9'.
The wire W is connected to the contact terminal as follows. First, one end portion of the wire W is laid on the rear end portion of the contact terminal 1' in such a manner that the one end portion of the wire W is in parallel with the rear end portion of the contact terminal 1'. Under this condition, the one end portion of the wire W is pushed in the slots 12' of the electrically conductive section 4' from the above. Accordingly, the right and left blades 11' cut the insulating cover of the wire W, and contact the conductor of the wire W. When the one end portion of the wire W is further pushed in, the conductor of the wire W is moved to be between the right and left blades 11', so that the conductor is more positively held by the right and left blades 11'. In this operation, a force is applied to the right and left blades 11' so that the blades are moved away from each other.
In general, a contact terminal is mass-produced, and a number of contact terminals are built in a connector housing in such a manner that they are adjacent to one another. Hence, there has been a strong demand for the provision of a contact terminal which is small in size, and light in weight. In order to decrease the weight of the contact terminal, it is essential to reduce the thickness of a metal plate which is formed into the contact terminal. And in order miniaturize the contact terminal, it is necessary to decrease the width and the length of the contact terminal. For instance, in order to decrease the width of the contact terminal, it is essential to decrease the width of the insulation piercing blades forming the slot.
However, if the thickness of the metal plate, which is a raw material for the contact terminal, is decreased, the width of the insulation piercing blades is decreased, then the mechanical strengthof the blades is also decreased, as a result of which, when the wire is pushed in the slot, the right and left blades are opened outwardly.
In view of the foregoing, in the conventional contact terminal shown in FIG. 7, the insulation piercing blades 11' are respectively formed by bending inwardly the front and rear end portions of the side walls 9' of the electrically conductive section 4'. However, the force, acting on the blades 11' when the wire W is press-fitted into the slots 12', acts through the side walls 9' on the bottom wall to bend the bottom wall in a curved condition in a lateral (right-to-left) direction. Therefore, if the bending rigidity of the bottom wall is low, there is a possibility that the side walls 9' are bent outwardly, and accordingly, the blades 11' are bent outwardly.